从文件读取数据，文件名作为输入

I am writing a program which reads data from different files, which are given as input strings, and stores them into a vector of vectors. The problem I am not able to debug the loop which reads different files. I have closed the ifstream object, cleared the string using empty function... but still it just terminates when i give second file name as input.I am writing a program which reads data from di